High voltage generator for x-ray diagnosis apparatus

ABSTRACT

A high voltage generator for X-ray diagnosis apparatus includes a high voltage transformer with at least one primary winding connected to an alternating current net and at least one secondary winding feeding the X-ray tube as well as means adjusting the high voltage by changing the primary alternating voltage. These means are connected to a rectifier bridge located in the primary circuit of the high voltage transformer. The invention is particularly characterized in that these means are formed by a variable resistance connected to the outlet of the rectifier.

United States Patent [191 Romandi 51 Nov. 5, 1974 HIGH VOLTAGE GENERATOR FOR X-RAY DIAGNOSIS APPARATUS [75] Inventor: Denes Romandi, Erlangen, Germany [73] Assignee: Siemens Aktiengesellschaft,

Munchen, Germany [22] Filed: Nov. 16, 1973 [21] Appl. No.: 416,354

[30] Foreign Application Priority Data Nov. 27, 1972 Germany 2258085 [52] U.S. Cl 250/402, 250/408, 250/421 [51] Int. Cl H05g l/20 [58] Field of Search 250/421, 409, 408, 402

[56] References Cited UNITED STATES PATENTS 2,514,935 7/1950 Clapp 250/408 11/1968 Russ ..250/408 2/1971 Takao ..250/402 Primary Examiner-James W. Lawrence Assistant Examiner-C. E. Church Attorney, Agent, or Firm-Richards & Geir [57] ABSTRACT A high voltage generator for X-ray diagnosis apparatus includes a high voltage transformer with at least one primary winding connected to an alternating current net and at least one secondary winding feeding the X-ray tube as well as means adjusting the high voltage by changing the primary alternating voltage. These means are connected to a rectifier bridge located in the primary circuit of the high voltage transformer. The invention is particularly characterized in that these means are formed by a variable resistance connected to the outlet of the rectifier.

4 Claims, 4 Drawing Figures SHEET 1 [)F 2 Fig.4

HIGH VOLTAGE GENERATOR FOR X-RAY DIAGNOSIS APPARATUS This invention relates to a high voltage generator for X-ray diagnosis apparatus which contains a high voltage transformer with at least one primary winding connected to an alternating current net and at least one secondary winding feeding the X-ray tube, as well as means adjusting the high voltage by changing the primary alternating voltage which are connected to a rectifier bridge located in the primary circuit of the high voltage transformer.

In a known high voltage generator of this type a direct voltage source is used for adjusting the high voltage. It lies in the zero branch of the rectifier bridge and has a variable clamping voltage. The direct voltage source consists of a sieve chain which can be charged by an electronic switch. The capacitive voltage of this sieve chain is opposed to the rectifier voltage. A drawback of this high voltage generator is that there is a comparatively large delay with which the X-ray tube voltage follows an adjusting signal or a regulating signal, since to change the X-ray tube voltage it is neces sary to change a condenser charge which takes place according to an exponential function with a predetermined time constant.

An object of the present invention is to provide a high voltage generator of the described type wherein the X-ray tube voltage follows much faster an adjusting signal or a regulating signal than was possible in prior constructions.

Other objects of the present invention will become apparent in the course of the following specification.

In the accomplishment of the objectives of the present invention it was found desirable to make the adjusting means from a variable resistance connected to the outlet of the rectifier. Then the resistance value of this variable resistance determines the X-ray tube voltage. Since the capacities in the primary circuit of the high voltage transformer can be kept considerably smaller than was possible in prior art, the adjustment or regulation of high voltage at the X-ray tube can take place very quickly.

The adjusting and regulating speed can be still further increased when the variable resistance is constituted by an electronic switch which is switched with a frequency and a key ratio corresponding to the rated value of the X-ray tube voltage. If, for example, in that case the X-ray tube voltage will exceed its rated value, then it is possible by opening the electronic switch, namely, by switching off in its high ohmic condition, to provide a very quick return to the rated value. In a re verse case a very quick balancing is also possible.

The invention will appear more clearly from the following detailed description when taken in connection with the accompanying drawings showing by way of example only, preferred embodiments of the inventive idea.

In the drawings:

FIG. 1 is a circuit diagram of a high voltage generator of the present invention.

FIG. 2 is a diagram showing the time flow of voltage at the adjusting means for high voltage of FIG. 1.

FIG. 3 shows details of the circuit diagram of FIG. 1.

FIG. 4 is a diagram showing the voltage flow at the outlet of the operational amplifier in FIG. 36

The high voltage generator shown in FIG. 1 includes a high voltage transformer with a primary winding 1 and a secondary winding 2. The primary winding 1 can be connected to the feed net. The secondary winding 2 feeds an X-ray tube 3 through a high voltage rectifier 4. The primary winding 1 is connected to a rectifier bridge 5 the direct voltage of which is supplied to an adjusting resistance 6.

The adjusting resistance 6 determines the high voltage of the X-ray tube 3. The voltage of the X-ray tube follows very quickly a change in the resistance 6 since adjusting and regulating delays are very short.

According to a preferred embodiment of the present invention the adjusting resistance 6 consists of an electronic switch 7 shown by broken lines in FIG. 1, which replaces the resistance 6 and which is switched on with a frequency and key ratio corresponding to the rated value of the X-ray tube voltage. The rated value of the X-ray tube voltage is set for voltage regulation at a rated value giver 8 and a corresponding signal is supplied to a comparison member 9. The comparison member 9 also receives an actual value signal obtained from a voltage divider 10. The comparison member 9 opens and closes the electronic switch 7 depending upon the deviation of the actual value of the X-ray voltage from its rated value.

These conditions are closer indicated in FIG. 2. FIG. 2 is based on the assumption that at time zero the operation of the high voltage generator is started. At time zero the voltage of the X-ray tube is still zero, so that the switch 7 is closed by the comparison member 9. The voltage at the switch 7 drops to the value Ul which corresponds to the rated value of the X-ray tube voltage. When the voltage Ul is reached the switch 7 is opened, i.e. high ohms, and its voltage rises due to the hysteresis of the comparison member 9 up to the value U2. When the value, U2 is reached, the switch 7 is closed again and the described procedure is repeated. Thus the voltage in the switch 7 swings back and forth between the values U1 and U2. The voltage in the X-ray tube 3 runs correspondingly. The voltages U1 and U2 are so fixed that there is no undesired deviation of the X-ray tube voltage from its rated value.

If the X-ray tube 3 is switched off at the time t1, then the voltage at the switch 7 rises to its highest value, as indicated in FIG. 2.

The removal of deviations of X-ray tube voltage from its rated value take place very quickly since the key ratio and the frequency with which the switch 7 is opened and closed, are set depending upon the deviation of the actual value of the X-ray tube voltage from its rated value. The switch 7 can be a transistor or an electronic switch with ignition characteristic, for example, a thyristor.

In the high voltage generator shown in FIG. I the switching on and off of the X-ray tube 3 is possible in a simple manner by setting the rated value as zero at the rated value giver 8 for switching off the X-ray tube 3 and setting the desired rated value for switching on. The rise and drop of the Xray tube voltage during switching on and off take place also within comparatively short time periods.

Within the framework of the present invention the resistance 6 or the electronic switch 7 can be component parts of a regulating circuit for the dose output of the X-ray tube which contains as the actual value giver a ray measurer for the X-rays. This ray measurer then replaces the voltage divider 10. In that case also there is a quick removal of deviations of the dose output of the X-ray tube from its rated value by changing the X-ray tube voltage.

FIG. 3 shows in detail the structure of the comparison member 9 and the switch 7. The comparison member 9 includes an operational amplifier 11 having an inlet 12 receiving a signal from the voltage divider 10 through a coupling resistance 13. The amplifier has another inlet 14 receiving a signal taken from the rated value giver 8 through the coupling resistance 15. The operational amplifier 11 has a hysteresis characteristic such that its voltage at the outlet 16 has a constant'positive value so long as the voltage at the inlet 12 is smaller than at the inlet 14. When the voltage at the inlet 12 exceeds the voltage at the inlet 14, the voltage at the outlet 16 moves to a negative value and remains constant until the voltage at the inlet 12 again drops below the voltage 14 by a predetermined amount. When there is positive voltage at the outlet 16, the transistor 17 which constitutes the switch 7 is open, while in case of negative voltage it is closed.

Thus when the X-ray tube voltage has not reached yet its rated voltage and therefore the voltage at the inlet 12 is smaller than at the inlet 14, the transistor 17 is closed, i.e. has low ohms. The X-ray tube voltage therefore increases until the voltage at the transistor 17 has reached the value U1. At that moment the voltage at the outlet 16 jumps from its positive value U3 (HO. 4) to its negative value U4. Consequently the voltage at the transistor 17 rises again at the time period t2 until it reaches the value U2 at the time period t3. At that time the voltage at the outlet 16 again jumps from the negative value U4 to the positive value U3 and keeps it until the time t4. The further voltage run at the transistor 17 and the outlet 16 of the operational amplifier 11 is illustrated in FIGS. 2 and 4.

I claim:

1. A high voltage generator for X-ray daignosis apparatus for use with an X-ray tube and a source of alternating current, the generator comprising a high voltage transformer having at least one primary winding connected to said source and at least one secondary winding connected to said X-ray tube, a circuit connected to said primary winding and having a rectifier bridge, and adjusting means connected with said rectifier bridge for high voltage by changing the primary alternating voltage, said adjusting means consisting of a variable resistance connected to the outlet of the rectitier.

2. A high voltage generator according to claim 1, wherein said variable resistance consists of an electronic switch, said switch being adapted to be switched with a frequency and pulse duty factor corresponding to the rated value of the X-ray tube voltage.

3. A high voltage generator according to claim 1, having a regulating circuit for the X-ray voltage and a rated value transmitter, said adjusting means constituting a part of said regulating circuit, said rated value transmitter being used for the X-ray tube voltage as a switch off, in that the rated value is set as zero for switching off.

4. A high voltage generator according to claim 1, having a regulating circuit for the dose output of the X-ray tube, said adjusting means constituting a part of said regulating circuit, said regulating circuit including a ray measuring device for the X-rays constituting an actual value transmitter. 

1. A high voltage generator for X-ray daignosis apparatus for use with an X-ray tube and a source of alternating current, the generator comprising a high voltage transformer having at least one primary winding connected to said source and at least one secondary winding connected to said X-ray tube, a circuit connected to said primary winding and having a rectifier bridge, and adjusting means connected with said rectifier bridge for high voltage by changing the primary alternating voltage, said adjusting means consisting of a variable resistance connected to the outlet of the rectifier.
 2. A high voltage generator according to claim 1, wherein said variable resistance consists of an electronic switch, said switch being adapted to be switched with a frequency and pulse duty factor corresponding to the rated value of the X-ray tube voltage.
 3. A high voltage generator according to claim 1, having a regulating circuit for the X-ray voltage and a rated value transmitter, said adjusting means constituting a part of said regulating circuit, said rated value transmitter being used for the X-ray tube voltage as a switch off, in that the rated value is set as zero for switching off.
 4. A high voltage generator according to claim 1, having a regulating circuit for the dose output of the X-ray tube, said adjusting means constituting a part of said regulating circuit, said regulating circuit including a ray measuring device for the X-rays constituting an actual value transmitter. 